Manufacturing method of a magnetron anode

ABSTRACT

A method for manufacturing an anode structure used for a magnetron from metal stock, by which the peripheral wall and the inner vanes of the anode are integrally constructed, the said method comprising three steps, that is: the step of forming a primary workpiece consisting of a thick cylindrical wall and a thick disk-like part closing the cylinder in its axially mid portion, the step of forming a secondary workpiece from the primary workpiece by a warm extruding process so that the secondary workpiece has a plurality of radial vanes integral with the cylindrical wall and extending radially inward from the wall, and a step of removing the remaining portion of the disk-like part bridging the bottom ends of the vanes.

United States Patent Akeyama et a1.

[ 51 July 25, 1972 [$4] MANUFACTURING METHOD OF A MAGNETRON ANODE [72] Inventors: Masamoto Akeyama, Kokubunji; Sohjl Taltahashi, Kodaira, both of Japan 2,674,784 4/1954 Roberts et'aL... ....29/597 2,688,793 9/1954 Carlson ..29/597 3,293,487 I2/l966 Pickering ..3l5/39.65

OTHER PUBLICATIONS Handbook of Engineering Fundamentals, Second Edition, John Wiley & Sons, lnc., NY, 1952. TAlSlES 1952 C3. P. 12- 42.

Mechanical Engineers Handbook, McGraw-Hill Book Co., N.Y., 1964. TJ15| M37 I958 C.9. P. 6-82.

Primary ExaminerR. Spencer Annear Attorney-Craig, Antonelli and Hill [57] ABSTRACT A method for manufacturing an anode structure used for a magnetron from metal stock, by which the peripheral wall and the inner vanes of the anode are integrally constructed. the said method comprising three steps, that is: the step of forming a primary workpiece consisting of a thick cylindrical wall and a thick disk-like part closing the cylinder in its axially mid portion, the step of forming a secondary workpiece from the primary workpiece by a warm extruding process so that the secondary workpiece has a plurality of radial vanes integral with the cylindrical wall and extending radially inward from the wall. and a step of removing the remaining portion of the disk-like part bridging the bottom ends of the vanes.

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zsr/oH/z MIA/[NUMBER INVENTORS and soHJ'I TA kA HASHI MASAMaT'a AKEYAMA PATENTED JULZSIHIZ SHEE! 0F 4 GE 658mg Q T QM H INVENTORS MASAMDTO AkEYAMA and SOHJI TAKAHASHI MANUFACTURING METHOD OF A MAGNETRON ANODE This invention relates to a method of manufacturing an anode structure used for a magnetron.

The magnetron is widely used as a microwave oscillation tube in the fields of microwave communication and for microwave heating. Almost all magnetrons now in use are of the multi-split anode type. The anode structure of such a type of magnetron has a hollow cylindrical wall and a large number of plate-shaped partitions (hereinafter referred to as vanes) extending radially inward from the cylindrical wall to form resonant cavities therebetween. The common material for the anode is copper. As the physical dimensions of the resonant cavities directly affects the oscillation frequency of a magnetron oscillator, it is very important that the vanes defining the cavities are accurately formed and positioned.

However, in magnetrons commonly found on the market, for example, magnetrons for electronic cooking ranges, the anode has a number of (usually l and odd) vanes jointed to a separately prepared cylindrical wall by means of solder or the like. Such a conventional method for making an anode of magnetron has the following disadvantages; that is, l the diffusion method of soldering, as is usually adopted for the present purpose, requires a large quantity of expensive solder; (2) the soldering operation is complicated and annoying because of the large number of work points, that is, because l0 and odd vanes must be soldered one by one; (3) it is unsuited for the mass production, the setting-up of assembly jigs consumes many man-hours; (4) the produced anodes will suffer a high rejection rate, as the dimensions of the cavities cannot be made sufficiently accurate and are not sufiiciently uniform among the products; and (5) the produced anodes are subject to inferior electric characteristics because of the solder adhering to the walls of the cavities which increases the electric resistance of the resonator.

Another known manufacturing method of a magnetron anode, called cold hobbing method," is disclosed in an article by Alex Phillips titled How Cold Hobbing Shapes Intricate Parts" published in the periodical The Iron Age, Apr. 3, I958, pp 9l-93. Although this known method is suitable for manufacturing a magnetron anode having a satisfactory electric characteristics, it is inferior in its utility factor regarding the use of raw material, requires a long processing time and is conducive to causing a very short operation life of the hobs. Accordingly, this known method also has the disadvantage that the manufacturing cost with this method is the same as or higher than with the previously described soldering method, it being too high for a magnetron for ordinary use.

The object of this invention is to solve the above-described problems encountered in the known method and to provide a manufacturing method of a magnetron anode, which is simple in operation and ensures yield of highly accurate products.

In order to achieve the above object, the method of this invention is characterized in that the cylindrical wall and vanes of a magnetron anode are integrally formed through a warm extruding process from a primary workpiece prepared in a predetermined shape and dimensions.

More inclusively, the manufacturing method of a magnetron anode according to this invention comprises the following three fundamental steps: that is, the first and preliminary step of forming a primary workpiece from an appropriate metal sock so that the said primary workpiece has a cylindrical wall and a disk-like part laterally bridging the inner or space of the cylinder; the second and the main step of forming a secondary workpiece from the said primary workpiece by a warm extruding process so that the said secondary workpiece has a plurality of radial vanes integral with the cylindrical wall and the said disk-like part and extending radially inward from the wall; and the third and final step of removing the reduced and remaining disk-like part bridging the lower ends of the vanes.

According to the method of this invention which consists of the above-mentioned three fundamental steps. a magnetron anode structure having accurate dimensions and therefore excellent electrical characteristics is obtained through a simple process and at low cost.

Other objects, features and merits of this invention will be clarified in the following description given in connection with an embodiment of this invention and with reference to the accompanying drawings, in which;

FIG. 1 is a plan view of a typical magnetron anode;

FIG. 2 is a sectioned vertical view of the same anode made by the conventional method;

FIG. 3 is a corresponding view of such an anode made by the method of this invention;

FIGS. 4a to 4d are sectioned vertical views showing the steps in the manufacturing method of a magnetron anode according to this invention;

FIG. 5 is a sectioned vertical view of the essential portion of a extruding machine used for executing the first step of the method, shown with a primary workpiece therein;

FIG. 6 is a similar view of the extruding machine in the second step with a secondary workpiece therein;

FIG. 7 is a partly broken side view of the extruding punch (or hob) shown in FIG. 6;

FIG. 8 is a sectioned view of the same extruding punch (or hob) seen at the line VIII-VIII.

FIG. 9 is a graph showing results of the dimensional tests on the vane gaps of magnetron anodes; and

FIG. I0 is a graph showing the Q factors of resonant cavities of magnetron anodes.

As typically shown in FIG. I, commonly available magnetron anodes such as the ones for electronic ranges (cooking ovens utilizing the microwave heating) have a number of (for example, 12) vanes 2 extending radially inward from a thick cylindrical wall 1 so as to constitute the resonant cavities 3 between the vanes. In the center of the cylinder is left a cylindrical vacant space 4 into which a cathode (not shown) is to be inserted.

In the conventional manufacturing method of such a mag netron anode, the cylindrical wall 1 and the vanes 2 are separately made in a preliminary stage, and then the vanes are soldered to the inner face 5 of the wall I to complete the anode, as shown in FIG. 2. Such a fabricating operation is very complicated and therefore requires considerable man-hours, and yet does not assure the sufficient accuracy in the physical dimensions of the completed anode structure.

According to the method of this invention, the vanes are squeezed out, by means of an extruding machine, from a primary workpiece which consists of a cylindrical wall and a disklike part closing the hole of the cylinder in the mid portion thereof. The thus formed vanes 2 are integral with the wall 1 in the structure, as shown in FIG. 3. The magnetron anode produced through such a simple process has very accurate dimensions and satisfactory electrical properties.

An example of the manufacturing method of this invention will be described in detail hereunder with reference to FIGS. 40, 4b, 4c and 4d which show axially sectioned vertical views respectively of a metal stock a, the primary workpiece b, the secondary workpiece c and the finished product d as a magnetron anode. Copper (preferably non-oxygen copper) is the commonly used material.

According to the fundamental concept of this invention, the primary workpiece b may be formed from a metal stock of 0ptional shape and by any known method such as cutting, casting, swaging or the like. In the following description, however, the primary workpiece b as shown in FIG. 4b is formed from a thick copper disk 0 as shown in FIG. 4a by the cold extrusion, by way of example.

In the first and preliminary step of the process, the primary workpiece b is formed, as mentioned above, from a thick copper disk a by means of a cold extruding machine so that the workpiece b has a thick cylindrical wall I and a thick disk like part 6 bridging the mid portion of the inner face of the cylinder in such a manner that the vertical section of the workpiece is of an approximate H-shape. In the second and main step, the primary workpiece b undergoes a warm extrusion to become the secondary workpiece c. That is, a number of vanes 2 are extruded from the disk-like part 6, the vanes 2 being extending radially inward from the wall 1 and integral with the wall 1 as well as the remaining portion 6a of the disk-like part 6 as shown in FIG. 40. In the third and final step of the process, the remaining portion 6a of the disk-like part 6 is removed by cutting to thereby produce a finished magnetron anode, as shown in FIG. 4d.

The first step of the process will be described in still more detail with reference to FIG. 5. In the Figure, reference numeral designates a hollow cylindrical die, II a lower punch, and [2 an upper punch. The lower punch 11 has a portion Ila of smaller diameter separated by a step portion Ilc from the main body 11b of the punch. Numeral l4 designates the clearance between the punches 1!, I2 and the die 10. The figure shows the state wherein the upper punch 12 has been driven down and the primary workpiece b has been formed between the tools II], II and I2.

An example of the dimensions of the tools shown in FIG. 5 are as follows:

Inner diameter of the die [0 48.50 mm Diameter of portion 1 In of punch ll 38.50 mm Dia. of main body In of punch I! 48.45 mm Height ofponion [in of punch I] 10.00 mm Diameter of upper punch [2 38.50 mm For the raw material, a non-oxygen copper disk 48.45 mm in diameter and I6 mm in thickness was used.

In the operation, firstly the copper disk 0 is placed within the die I0 and between the lower punch 11 and the upper punch 12. It is preferable to apply a paste of molybdenum disulphide (for example) on the surfaces of the copper disk a and on the inner face of the die I0 as the lubricant. Then the upper punch 12 is pressed down into the disk a by means of a I60 ton punch press. Under this intense pressure, the material of the disk 0 exhibits plasticity, and a portion of the material is extruded in axial direction into the clearance [4 to form the cylindrical wall 1. This extrusion is done in the cold state, that is, at room temperature. In this example, the upper punch 12 is depressed by 8 mm from the original surface of the disk at with a pressure P of about 120 tons to make the resultant depth of the upper indentation 14 mm. The depth of the lower indentation is determined by the height of the reduced portion Ila of the lower punch II, it being [0 mm. It will be clear that the distance between the upper and lower punches is 8 mm in this state. Thus is formed the primary workpiece b which consists of a cylindrical wall I of 48.50 mm in outer diameter, 38.50 mm in inner diameter and 32 mm in height and a disklike part 6 of 38.50 mm diameter, 8 mm in thickness and positioned at 14 mm and H) mm respectively from the top and bottom ofthe cylindrical wall I.

The above!-described extruding process imparts an appropriate hardness to the primary workpiece, which is advantageous for the second and main step of this manufacturing method and which also increases the strength of the produced magnetron anode.

In the concept of this invention, however, the method for making the primary workpiece is not limited to the abovedescribed one. Generally, as already mentioned, the primary workpiece b may be formed from a copper piece of optional shape and by optional method such as cutting, casting or any other known tooling method. Moreover, the wall 1 and the disk-like part 6 of the primary workpiece are not required to be necessarily integral. Because, if the wall 1 and the disk-like part 6 are not integral, they are compulsively rendered integral in the next stage of the process. Further, the vertical section of the primary workpiece b need not necessarily be of an approximate H-shape. It is only essential for the primary workpiece to have a hollow cylindrical wall I and a disk-like part 6, the position of the disk-like part 6 along the axis of the cylinder being considerably optional. All such modifications are within the scope ofthis invention.

Now, the second and main step of this method is described in detail with reference to FIG. 6 which illustrates formation of the secondary workpiece c from the above-described primary workpiece b using a hob 13 in a warm extruding process. The hob 13, as shown in FIGS. 7 and 8, has a generally cylindrical shape and is provided, at one end thereof, with l2 slots 13b equi-spaced around the cylinder and cut radially inward from the periphery, thereby forming teeth 13c between adjacent slots. The teeth 13c are connected with the central part 13a.

One example of the dimensions of such a hob is 38.50 mm in diameter, 10 mm in diameter of the central part l3a, 1.6 mm in the width of the slots 13b and 10 mm in the axial depth of the slots. The die 10 and the lower punch 11 shown in FIG. 6 are the same in shape and dimensions as those shown in FIG. 5 respectively.

In the operation, a paste of molybdenum disulphide is first applied onto the surfaces of the primary workpiece b and on the teeth 13c of the hob 13, and then the primary workpiece b is placed in the die [0 and between the hob l3 and the lower punch 11. This assembly is externally heated by a suitable heating method until the temperature of the primary workpiece b is raised to 200 :10" C. Then the hob i3 is depressed into the primary workpiece b to extrude a part of copper from the disk-like part 6 into the slots 13b of the hob l3 and the clearance 14 between the die 10 and the hob [3. In this example, the hob 13 is pressed down by 4 mm from the original surface of the disk-like part 6 with a pressure P of approximately I20 tons. Thus, the 12 slots of the hob l3 are filled with copper to fonn as many vanes, and the surplus copper is further extruded radially to thereby make the vanes 2 integral with the cylindrical wall I and to increase the height of the wall 1 by approximately 6 mm, making the total height of the wall 38 mm. Therefore, even if the wall I and the disk-like part 6 have not been made integral in the primary workpiece b, they will become integral after the above-described process of the second step. The secondary workpiece c as shown in FIG. 4c is thus obtained.

The above-described warm extruding process is very effective method to form thin and axially elongated vanes and is the most important step in the method of this invention. By such warm extruding process, vanes having dimensions of higher accuracy than those obtained by the cold extrusion are achieved. Moreover, this method ensures the uniformity of the finished products, small loss of the material and a long opera tion life of the hob.

Finally, in the third and last step of the process, the remaining disk-like part 6a (approximately 4 mm thick) bridging the bottoms of the vanes 2 is cut off by a known cutting machine such as a lathe or a milling machine to thereby complete the anode structure which has vanes integral with the wall.

According to the manufacturing method of this invention as described hereinbefore, a magnetron anode having high dimensional accuracy and therefore excellent electrical properties is obtained. For example, FIG. 9 shows a test result of the vane gaps, that is, the distances between the inner edges of adjacent vanes of a magnetron anode with a cylindrical central space 4 of l0.00 mm in diameter, the abscissa indicating the vane numbers and the ordinate the vane gap in mm. The solid line a shows the test result of an anode manufactured by the method of this invention, while the dash line 1) indicates the test result of an anode manufactured by the conventional soldering method. This diagram clearly shows that the errors in vane gaps are in the range of i005 mm with the method of this invention, whereas those with the conventional method are in the range ofiO. 10 mm, the former being one half of the latter. Thus, the method of this invention ensures a very high dimensional accuracy.

FIG. 10 shows Q values of the resonant cavities 3 formed between adjacent vanes of magnetron anodes, the abscissa indicating deviation of frequency from the resonant frequency in Me and the ordinate the voltage standing wave ratio (abbreviated as V.S.W.R. The curves 0 and b respectively represent values for magnetron anodes manufactured by the methods of the present invention and the conventional soldering method, Q values of the resonant cavities determined from FIG. being 1,440 and 1,090 respectively for the former and the latter cases. That is, the Q value can be raised approximately 32 percent above the prior level by the method of this invention.

The merits of the method of this invention are summarized as follows:

I. The anode can be formed having very accurate vane gaps and therefore very accurate resonant cavities.

2. As the operation is simple and the dimensions of the products are uniform, the process is suitable for a mass production system.

3. Q value of the resonant cavities is improved as much as 32 percent asshown in FIG. 10.

4. The cavity loss can be decreased by approximately 30 percent.

5. The production cost of the anode can be reduced by approximately 40 percent.

6. Long operation lives of the tools (especially the hob) are ensured.

We claim:

1. A manufacturing method of a magnetron anode comprising the step of forming a primary workpiece from an appropriate metal stock so that said primary workpiece has a hollow cylindrical wall and a disk-like part laterally bridging the inner space of the cylinder, the step of forming a secondary workpiece from said primary workpiece by a warm extruding process so that said secondary workpiece has a plurality of vanes which extend radially inward from said cylindrical wall and are integral with said wall and said disk-like part, and the step of removing the remaining disk-like part bridging the ends of said vanes.

2. A manufacturing method of a magnetron anode as defined in claim 1, wherein said primary workpiece is formed from a disk-shaped metal stock by a cold extruding process.

3. A manufacturing method of a magnetron anode as defined in claim 2, wherein said disk-shaped metal stock is a thick copper disk and said primary workpiece is formed so that said disk-like part is positioned approximately at the middie of the axial length of the cylinder in such a manner that a vertical section including the axis of the cylinder assumes the shape of the letter H.

4. A method of manufacturing a magnetron anode as defined in claim 1, wherein the removal of the remaining disklike part is performed by cutting. 

1. A manufacturing method of a magnetron anode comprising the step of forming a primary workpiece from an appropriate metal stock so that said primary workpiece has a hollow cylindrical wall and a disk-like part laterally bridging the inner space of the cylinder, the step of forming a secondary workpiece from said primary workpiece by a warm extruding process so that said secondary workpiece has a plurality of vanes which extend radially inward from said cylindrical wall and are integral with said wall and said disk-like part, and the step of removing the remaining disk-like part bridging the ends of said vanes.
 2. A manufacturing method of a magnetron anode as defined in claim 1, wherein said primary workpiece is formed from a disk-shaped metal stock by a cold extruding process.
 3. A manufacturing method of a magnetron anode as defined in claim 2, wherein said disk-shaped metal stock is a thick copper disk and said primary workpiece is formed so that said disk-like part is positioned approximately at the middle of the axial length of the cylinder in such a manner that a vertical section including the axis of the cylinder assumes the shape of the letter H.
 4. A method of manufacturing a magnetron anode as defined in claim 1, wherein the removal of the remaining disk-like part is performed by cutting. 